Natural water may be contaminated with industrial wastes that contain toxic end products. Further, pesticides used for protecting crops may also be washed into and contaminate the water supply. These toxic chemicals have been found to create health hazards and also to damage/destroy various ecosystems.
A class of bacteria that may be found in water supply includes coliforms. Indeed, coliforms are a commonly-used bacterial indicator of the sanitary quality of foods and water. The presence of coliforms may be used to indicate that other pathogenic organisms of fecal origin may be present. This is because feces from warm blooded animals or human beings often leads to the contamination of water by coliforms and other pathogenic organisms.
Coliforms include E. coli, Salmonella, Klebsiella and Erwinia. These pathogenic organisms may cause intestinal infections, dysentery, hepatitis, typhoid fever cholera etc. Further, coliforms and other chemical contaminants may have toxic effects on the habitants of a contaminated pond/lake, limiting their growth and proliferation.